Electric selecting switch



g- 1935- D. A. CHRISTIAN I 2,010,348

ELECTRIC SELECTING SW'ITCH Filed June 14, 1935 4 Sheets-Sheet l DA wo 40AM" 6196/37/14 1935- D. A. CHRISTIAN 2,010,348

EPEGTRIC SELECTING SWITCH Filed June 14, 1933 4 sheets-sheet 2 reffi be? 3K CA4 bdl F 2? iii f Aug. 6, 1935. DL-A. CHRISTIAN ELECTRIC SELECTING SWITCH 4 Sheets-Sheet s Filed June 14, 1933 DAV/0 ADAM 639mm %%@wm r Aug. 1935. o. A. CHRISTIAN ELECTRIC SELECTING SWITCH Filed June 14, 1953 4 Sheets-Sheet 4 mm a i &

Patented Aug. 6, 1935 UNITED STATES PATENT OFFICE signor to Siemens Br others & Company Limited, London, England Application June 14, 1933, Serial No. 675,665 In Great Britain July 1, 1932 '1 Claims.

The invention relates to electrical selective systems such as automatic telephone systems, remote control systems and the like.

It is concerned with the selection of one of a number of circuits radiating from a centre. The

control of the selection at such centre may be exercised from a point remote from the centre which point may be referred to as the control point.

Preferably the selecting switch is, until stopped to eiiect a connection, in continuous movement and a feature of this invention is that a selecting switch is driven by a mechanism readily adaptable to local sources of electric power. For instance, if an alternating current supply is available the mechanism may be a driving motor of the synchronous type used for the driving of electric clocks.

In one application of the present invention it is arranged that, at the centre, a selecting switch, to contacts of which the several selectable circuits are connected, also acts to connect a circuit through to the control point as required, in other words the selecting switch acts as a call finder in response to some action in any one of the circuits, the driving means for the switch consisting of an alternating current synchronous motor.

In the case of an electric switch which is in continuous motion and acts as a call finder as well as a selector, a definite starting point is required from which a selection may be made.

It is arranged, as a feature of the invention, that the different type of electrical control required in the case of selection, as opposed to call, finder action, results from a variation of conditions under which current is supplied, atthe control point, to a line leading to the centre.

According to a further feature of the invention, an electrical selective system has a selective switch provided with a synchronous driving motor and circuit arrangements whereby the switch is normally maintained in continuous operation in order successively to test the condition, calling or passive of a number of selectable circuits.

Arrangements according to the invention as applied to telephone subscriber lines connected to a centre from which a circuit (control point line) continues to a telephone exchange will be described in connection with Figs. 1-4 of the accompanying drawings.

Of these drawings, Fig. 1 represents, diagrammatically the apparatus at the centre; Fig. 2 represents diagrammatically parts of the operating .mechanism, Fig. 3 shows the cam timing;

and Fig. 4, comprising the two parts Fig. 4a and Fig. 4b, shows a circuit arrangement at the control point suitable for use with the selecting switch.

The selecting switch of Fig. 1 is a continuously moving selector CS arranged to close spring contacts I and I, 2 and 2-to I2 and I2 by means of a cam, shown as CAI and CA2, operating thereon. The selecting switch is driven by a simple type of seli' starting alternating current synchronous motor MD, operated by current from 50 cycle alternating current mains, the circuit of the motor including certain normally closed relay and cam contacts, al, bI, 17112. Other contacts, as T3 and c, are connected across contacts aI, bl, bd2, in order that, under certain conditions, the motor circuit may be closed in spite of the fact that one of the contacts M, M, or bd2 may be open.

There is, included in one wire B of the line (hereafter called the control-point line) that joins the control point to the centre at which the selector is situated, (hereafter called the centre), a relay A adapted when operated to open at contact al the motor circuit and thus to arrest the motion of the motor, the operation of the relay being brought about as the selecting switch, in closing in turn the springs appropriate to the selectable circuits (hereafter called subscriber lines) closes the springs of a subscriber line that is in a calling condition, that is, is looped, the current for the relay being fed from the control point.

Correct centering is insured by means of a cam CA3, which operates on springs c to ensure that. though the motor circuit is broken at contact al, the motor shall not stop until the circuit is also broken at springs 0. Cam CA3 as well as that shown as CAI, CA2 may be taken to rotate in a clockwise direction.

The motor, on arrest, by means of the cam CAI, CA2, maintains the springs appropriate to subscriber lines closed, and thus maintains the subscriber line concerned in association with the control point over the control point line over which line the calling subscriber may, as by dialling, control the control point apparatus, relay A being rendered somewhat retarded in releasing by reason of rectifier AR connected in such manner as to present a high resistance to current flowing from positive connected to wire A to negative connected to wire B. It is thus conductive to current produced as a result of the dissipation of energy stored in the relay.

The selecting switch is arranged in one of its positions, which for convenience may be referred to as the normal position and which is numbered l in Fig. 1, to connect a relay B across the two wires of the control point line, this relay having in series with it a rectifier BR so connected that relay B will not operate with current flowing as above described, which may be regarded as the normal direction, and is the direction of flow (or rather the control point line polarity) when the control point is in a receptive, as distinct from an initiative condition. Relay B, when the control point is in an initiative condition, a condition which is indicated by a reversal of the controlpoint line polarity and which obtains when the control-point is calling a subscriber line, and when the selecting switch closes contacts I, l, operates, due to a reversed current, and at contact bl opens the circuit of motor MD. The selecting switch moves under the control of spring 0 until properly centered and during the slight movement that takes place between the opening of contacts bl and 0, contacts bet and bcZ which are brought into operative relationship with a cam CA5 Fig. 2 by the operation of relay B, are operated, and are cam held until the motor moves the selecting switch through position l2 in which position they are released. The loop across the control point line due to relay B indicates to the control point that the selecting switch is at its normal position whereupon current is withdrawn, by the control point, from the line and relay B is released and the motor is restarted. By reason of the operation, or rather of the cam holding of contacts bcl and Z102, relay B is maintained across the control-point line in spite of the fact that the switch moves from normal and would but for the said contacts out the relay from across the control-point line.

As soon as the exact period required by the selecting switch to reach the contact springs appropriate to the wanted subscriber line has elapsed, a period which can be measured by a synchronous and synchronized motor at the control point moving from a normal to a marked position, reversed current is again connected to the control-point line and relay B, being still across the line, will again operate and open the circuit of the motor which after centering under the influence of springs 0 will stop.

Relay B since it has now operated with the selecting switch in an off-normal position brings contacts bdl and mm into operative relationship with one of the projections a-7' 'on cam CA5, Fig. 2, and these springs are operated and held until the motor moves the selecting switch through position 52 in which position they are released. Springs bdl cut relay B from across the control point line and substitute therefor relay R, in series with which is a rectifier RR. which with the control-point line polarity reversed prevents relay R from operating. Springs bd2 maintain the circuit of the motor MD open since, relay B releasing, it would otherwise be closed at contact bl.

Due to the position of the selecting switch, the control point line is extended to the subscriber line and the latter, in a manner to be described in connection with Fig. 4, is run, relay R, being irresponsive to the ringing current.

At the end of the conversation the called subscriber hangs up and although relay R is across the line, by reason of rectifier RR being of high resistance to current in the reverse direction, signals the control point that the connection may be cleared. The control-point, in response to this signal, restores the control-point line polarity to normal relay R as a result thereof operating and at contact r3 closing the motor circuit. It also, at contacts 1'! and r2 opens points in the controlpoint line whereby, as the selecting switch drives towards normal, calling extension lines passed on the way shall not interfere with the apparatus. In position 62, that is in the prenormal position of the selecting switch, through switch position the switch moves without stopping, the cam held springs bcl and Z102, bell and bd2 are restored, the selecting switch being now again sensitive to calling lines.

If some or all of the subscriber lines are to be provided with metering facilities, the meters being situated at the control point, the control point is so arranged as will be described in connection with Fig. l, that, in order that the correct meter shall be connected to the metering circuit, when a calling subscriber line is extended to the control point a switch is rendered responsive to impulses representative of the identity of the calling subscriber line, the said switch after being set to an appropriate position in response to such impulses, causing the line current to be reversed whereby relay A is released and the selecting switch is restarted and driven to normal, in which position due to the reversed current, relay B operates to stop the selecting switch and to cause the operation of cam springs bcl and 1202.

The control-point now, in response to the loop placed across the control-point line, withdraws all current from the line and so releases relay B the selecting switch thus being again driven. After the elapse of the exact period required for the selecting switch to have reached the calling line, a period measured by a synchronous and synchronized motor (ME Fig. 4) in travelling from normal to a position marked by the impulse-set switch (AS), normal battery is reconnected to the line and if the switch AS is in fact set to the number of the calling subscriber line and as a consequence switch CS has reached the looped subscriber line, relay A operates and stops the motor.

The subscriber line is switched through to the 1st group selector and the call may then proceed in the usual normal manner. When the extension clears, relay A releases and the motor MD rotates to position 2 with all line potential removed as will be explained.

If the selecting switch had found no loop, due to the calling subscriber having hung up or to his having dialled a number other than his own, relay A would have failed to operate and the selecting switch would have driven to its pre-normal position.

The timing of the selecting switch may, perhaps, be more conveniently followed by reference to diagrammatic sketch Fig. 3, in which the moving parts CAI, CA2, CA3, CA6, and CA5 are represented as occupying the position referred to as normal or position i, that is the position in which cam CA9, CA2 operates number i set of springs and connects relay B to the control-point line. Relay B, (as described in connection with Fig. l) operates and opens the motor circuit (at contact bl of Fig. 1). The circuit of the motor is, however, maintained closed by springs 0 until these springs are opened at cam recess 5. Relay B, in addition, moved trigger tr l into the path of the projection on cam CA4 so that during the overrun of the motor, trigger tr l closes springs bcl and M2. During this overrun, if the trigger is in the path of cam CA4, the supporting piece bsp is lifted onto ramp bar (as will best be seen .in Fig. 2). The motor can now rotate in :the manner described and :the relay B will be main- :tained in connection with the control-point line until the gap in the ramp, passing position sl2, allows .bsp to dropback to its normal position.

Similar cam action can be seen to take place with reference to contacts bd and cam'CAS, except that these contacts cannot be operated in position i by reason of there being no projection on cam. CA5 in that position. If, however, relay B is operated, when the switch has moved into any of the positions 2'H, with one of the cam projections a--i near to trigger tr5, springs bdl and 22612 will be operated during the motor overrun. In Fig. 2, relay 'B is shown as provided with an armature ab having an extension cm which carries triggers inland trz'a and which abuts against contact spring bl. If relay B is energized, it attracts its armature ab thus moving trigger tr4 into the path of cam projection CA4. The cam operates th trigger and lifts supporting piece bsp which, riding against the under slope us of ramp her, is forced to the right until, finally, when it is lifted sufficiently 'high to become free of the under slope, it springs back to the left, but above, or rather upon the flat surface of ramp bcr.

Circuit arrangements, suitable for use at the control point, under the supposition that the switch is to be used in connection with a telephone system ar shown in Fig. 4. In this figure for convenience of finding contacts the circuit elements have been numbered Ei-El2.

The control-point line is provided with apparatus whichcomprises' (a) a number of relays (b) a uniselector, represented by its wipers ASIAS4 and by its driving magnet ASDM and (c) a synchronous motor switch repr sented by contacts smi (E3) smZ (El),sm3 (Elfi) and sand to smlfi (El l) of which only sm4sm5 are .shown, and by its motor ME. This motor switch be, generally, similar to that at the centre. Its contacts cm! to sm3 are respectively in the condition shown in Fig. l when the switch is passing through position I, and upon leaving that position they reversed. Its contacts sml sml3 are closed successivelyas the switch passes through positions 2-l i. This motor switch is normally at rest.

The control-point line can be, when in a receptive condition, extended by a line finder operating on terminals Al, Bi, Pi and Ml. It can be selected by a final selector ES (El), operating on terminals A2, B2, and P2.

An incoming call, that is a call initiated at .a subscriber station, will first be considered.

It will be seen that the line polarity is as indicated in Fig. 4, that is positive from earth, through winding (II) of relay D, over contacts bait and 003 at rest, i6, k'rl, k5,,f6, (:02, wire A, and negative through windings (I) of relays D and Q, over contacts lc l, f5, col to wire B.

- When motor MD, Fig. l, in the course of one of its revolutions, encounters a subscriber line which is in a callingcondition, a circuit is completed for relays D and Q, and for relay A at the centre, rectifier AR presenting a high 're sistance.

Relay A stops motor MD as described.

Relay D has no effect that need be noted.

Relay Q at contact ql (El) closes a circuit, over contact 1151.2 for retarded release relay BB, and over contacts M2 and nl (which are offnormal springs of uni-selector AS) for winding (I) of relay C. Although a circuit, similar to that for relay C, exists for winding (I) of relay BA, this relay does not operate since its operating time is greater than that'of relay BB.

Relays BB and C operate.

Relay BB, at contact bol (E2) earths wire P2 to guard the control point line; at contacts 17M and 17235 (El) isolates relay BA; at contact bbB prepares a holding circuit for relay C winding (II); and at contact bbll (El) guards relay D against later opening of contact 003.

Relay '0, at contact cl (El) further prepares its own holding circuit; and at contact 04 (El) connects dialling tone to the control point line.

The subscriber whose line has thus been extended to the control point, dials the number, on the centre, of his own line, and in response to the dialled impulses, relays D and Q release and re-operate, relay D producing no effect.

Relay 'Q, at its back contact (El) closes and opens the circuit of magnet ASDII and of winding (II) of relay C. At its front contact ql it intermittently opens the circuit of relays BB and C but these are retarded release relays.

Uni-selector AS takes a number or" steps de-' pending upon the number of times relay Q releases. At its first step it opens its off-normal contacts ni (El) whereby the circuit of winding (I) of relay C is opened, Relay C, however, holds in the circuit of magnet ASDM.

Wiper A83 provides an alternative earth for wire P2.

During dialling, relay A, Fig. 1, holds. as its release is retarded by the short-circuiting eiIect of rectifier AR.

At the end of the train of impulses, relay C releases, due to its circuit being held open at the back contact ql.

Relay '0, at contact 02 (E2) closes a circuit from earth, over contacts tit) and 02 at rest and Z2112 operated, through winding (I) of relay CO; and at contactc l (El) removes dialing tone.

Relay CO operates, and at contacts out and 002 (El), reverses the direction of current in the control-point line; at contact 003 opens a point I contacts; and at contact rail; closes a bridge across contact 003, also to maintain a circuit for relays D and Q.

Due to the reversal of the current in the control point line, relay A, Fig. 1, releases and at contact al recloses the circuit of motor MD. (Relays Q and D will also momentarily release). Motor MD will drive the switch at the centre to position I.

As soon as switch CS moves from the calling line, relays D and Q will release (as the switch moves towards position I it may connect the control-point line to other subscriber-lines which are in a calling condition. Relays D and Q will operate in circuit with such lines but will have .no effect. Relay A will not operate as such lines .are passed since the line polarity is reversed).

Relay Q, on releasing, opens the circuit of relay BB which releases.

Relay BB, released, at contact bbi! (E2) opens the circuit from contact till of winding (I) of relay CO; at contact 12% closes a circuit from earth, over contacts naZ, i253, etc., and ba winding (II) of relay CO, to hold this relay operated; and at contact bbl (E l) closes a circuit from earth, over contacts m5 and bb'i for winding (I) of relay J which operates.

Relay J, at contact 71! (E4) prepares a holding circuit for itself. This is a guard circuit and provides that if, due to the operation of relay Q as switch CS passes other calling lines, relay BB should operate, relay J will still be held. Contact 7'2 (E5) provides a holding circuit from earth at contact m2, for relay RA. If, in the above stated event, relay BB should operate and open the holding circuit of relay RA, there will still be a holding circuit for relay RA, provided by contact (15, relay D also operating as the switch passes calling lines.

Contact 9'4 (E2) opens the holding circuit through winding (II) of relay CO; contact 9'5 (E2) provides an alternative holding circuit through winding (I) of relay CO. If, in the stated event, relay BB should operate, relay CO will hold in a circuit from earth, over contacts H9, at, bb2, and its own winding (I). Contact y'l (El) guards relays D and Q; and contact 7'8 (El) opens the circuit of winding (II) of relay BA, this circuit being otherwise closed at contact 27215.

When switch CS reaches position I, a circuit will be closed from positive, through winding (II) of relay D, over contacts fl, 1116, k5, it, wire B of the control-point line, rectifier AR, contact r2, contact I of switch CS, contact boll, rectifier BR, relay B, contact I of switch CS, contact Tl, Wire A, contact coi, f5, l'c l, windings (I) of relays Q and D.

Relays Q and B will operate but the resistance of relay B is such that relay D will not operate.

Relay B, as described in connection with Fig. 1,

. stops the motor and is connected across the line.

Relay Q, at contact ql (El) closes the circuit for relay BB which again operates.

Relay BB, at contact 'bbZ (E2) holds winding (I) of relay CO, at contact bbl (E5) holds winding (I) of relay J to earth at contact t6; at contact bbfi (E5) opens the circuit of relay RA; at contact bbll) (E8) prepares a circuit for motor ME; and at contact bblS (El) prepares a holding circuit for itself.

Relay RA releases and at MS opens the circuit of relays D, Q and B; at contact m9 (E8) closes a circuit for motor ME; and at contact ml l (El) closes a holding circuit for relay BB.

Relays Q and B release, (relay D was not operated) Relay Q at contact ql opens the circuit of relay BB but an alternative circuit will shortly be closed.

Relay B recloses the circuit of motor MD as described.

Motors MD and ME now rotate in synchronism, the'former maintaining cam contacts bcl and bet closed, and the latter closing various contacts sm. Of these contacts those which will be referred to as smi, smt and sm3 remain closed until the motor reaches position l2, and those which will be referred to as sm, sm5, smt, etc., operate in turn as the switch occupies positions 2, 3, 4 etc. Contact smi (E3) changes over and opens the original start circuit of motor ME; it closes an alternative circuit from earth over contacts bblii, 1%, ti and sml. Contact 81122 (El) closes a circuit from earth, over contacts smZ, ml I, k8, bolt, and baZ for relay BB. Contacts sm4 (El l), sm5, smt, etc., in turn, connect earth to the contacts in bank ASE of switch AS which, it will be recalled, has been set by the calling subscriber to a position corresponding to his line number.

When motor ME reaches a position which corresponds to the calling line, that is to the setting of switch AS, a circuit is closed from earth over contact fit (El l) at rest, the appropriate contact sm l, c1125, smt, etc., Wiper AS2 in its set position, contacts bat, qt, 00%, t3 and winding of relay T.

Relay T operates and at contact ti (E8) opens the circuit of motor ME whereby the motor is brought to rest in a position depending on the number of the calling line; at contact t2 (Eli!) closes a circuit from earth, over contacts bal, and t2 for relay TT; at contact t3 (EH) closes a holding circuit for itself from earth at contact 7' it; at contact t5 (E5) opens a point in the circuit of relay RA against subsequent operation of contact ($5; at contact t6 (E l) opens the circuit of relay J which, however, does not immediately release; at contact if? (E?) opens to prevent closure (at contact tt l) of a circuit for winding (II) of relay J, at contact tit (E2) opens the circuit of relay CO which releases; at contact U2 (El) place a short circuit across relay Q to provide a balanced bridge circuit; and at contact tl3 recompletes the loop which, as motor MD has driven in synchronism with motor ME, is completed at the centre to the calling subscriber-line.

Relay 'IT has no present efiect. It closes, however, at contact tt2 (Elli), a holding circuit for itself.

Relay CO, at contacts col and 002, re-establishes the original direction of connection in the control-point line; at contact 003 re-establishes the original circuit for relay D; and at contact coil (El 5) restores relay 'I' to dependence on contacts 705, $1726, etc.

Relays D and A, the latter due to the direction of current in the control-point line being restored, operate.

Relay A opens the circuit of the motor MD and brings switch CS to rest in association with the calling line.

Relay D, at contact dl (ES), closes a circuit for winding (II) of relay Q and at contact (14 (E l) provides a holding circuit for relay J.

Relay Q, at contact g2 (EH2) closes a circuit for relay ST which is the starting relay for line finders, not shown, one of which hunts for the calling line, the line being marked at wire P! in a circuit which includes contact til (E3) and relay K. Relay Q at contact ql re-operates relay BB but without effect, at contact (13 (El 8) closes an alternative circuit for the holding of relay TT.

When a line finder shall have found the calling control-point line, relay K will operate.

Relay K, at contact kl (EH2) opens the circuit of relay ST; at contact 752 (E3) closes a holding circuit for itself; at contact k3 (E6) connects up the meter M of the calling subscriber, the correct one having been selected by wiper AS E; at contacts k t and k5 connects the control-point line wires B and A respectively to line finder wires BI and AI respectively and, at the same time disconnects relay D; at contact k3 (El l) opens the circuit of relay T which releases; at contact is! (EM) opens one of the holding circuits of relay TT; at contact k8 (El) opens the holding circuit of relay BB (which, however, holds at contact ql but without effect) and closes a circuit which includes contact $1012, for relay KR; and at contact k9 opens. a point. in the circuit of. motor ME against the release of contacts bbl 5v and tl.

Relay KR, at contact kr3 (E'!) opens a point in the. homing circuit of switch AS, against the release of contact bblZ.

The meter having been connected up, metering can be effected in any suitable manner.

Relays D and then Q (contact dl) (E9) release, contact ql opening the holding circuit for relay BB.

Belay T releases and, at contact t2 (El opens the alternative holding circuit of relay TT; and at contact t6 (E4) removes the holding circuit of relay J from dependence upon relay D.

Relay BB releases and at contact bb'l opens the circuit of relay J, which releases.

Everything is now dependent upon relay K, that is, ultimately upon the calling subscriber maintaining a loop on wires Al B l When, eventually,

the caller does hang up, in a manner well known earth is removed from wire Pl with the result that relay K will release and will, at contact k3 (E6), open the metering circuit; at contacts R4 and k5 (El) restore the control-point line connection towards relay D; at contact k8 (El) open the operating circuit of relay KR which, however, holds over contacts smZ, mall and M4; and at contact k9 close a circuit from 5i) cycle alternating current source for motor ME.

Relay A releases due to the subscriber hanging up, and re-closes the circuit of motor MD whereby the motor is again set into motion, and so continues until arrested as above described or as below to be described.

Motor ME rotates until it occupies its normal position with all contacts sm in their normal conditions. Contact 31212 opens the circuit of relay KR; which releases.

Relay KR, at contact krl (El) reconnects relays D and Q to the control-point line, and contact M3 completes the circuit for magnet ASDM.

Magnet ASDM drives switch AS to its normal position in which position the self drive circuit is opened at wiper AS I.

A connection to a line on the centre, Fig. 1, and the association of the control-point line with an extension as a called extension is brought about as follows:

Connection is made, by a suitable final selector, to the control point apparatus, at the terminals P2, A2, B2, and assuming the line to be free a circuit will during the fleeting test period be completed over wire P2 (E2), wiper AS3 in normal position, contacts bal l, bbl, 19172 and winding (I) of relay CO.

Relay CO operates and at contacts col and 002 (El) reverses the connections to wires A and B, this being, at present, a preparatory operation; at contact 003 disconnects the line until the circuit is ready; at contact 004 (El) closes a circuit through winding (II) of relay BA,this relay being, however, retarded in operation in order, at contact Dal? (El), to guard relay AA against ringing current; at contact 006 (E2), prepares a holding-circuit for itself, eventually to be closed at contact bat, over contacts tt3, etc, and M9 (first unoperated and then operated when 5 is included) to its winding (II).

Ringing will be tripped and the connection switched through, at the final selector, in the usual manner and eventually relay BA will operate.

Relay BA, at contact ba2 (ET) opens any possible circuit for relay BB; at contact bail (E2) brings contact q5 into the holding circuit of relay CO as described; at contact be! I (E2) returns busying earth to wire P2 at contact bcl2 (El) removes the short circuit from relay AA; and at contacts bal3 and bold (El) polarizes the control-point line as follows: bal3, bal, 003, 7'6, krl, k5, it, at rest and 002 operated, wire B. Negative is connected to wire A as. may be seen.

Relay AA operates in a circuit completed at the final selector, and at contact cal (El') opens the original circuit of relay BA and at the same time closes an alternative holding circuit through winding (1), and an operating circuit for relay C.

Relay C operates, and at contact cl prepares a holding circuit for itself in series with magnet ASDM of switch AS.

Meantime motor MD has been continuing to drive switch CS towards position I. If, in approaching position i, it passes extension lines that are a calling condition, it will not regard them as, due to the operation of relay CO, either there is no current until relay BA operates, or when relay BA operates, the direction of current is wrong for the operation of relay A. After the operation of relay BA, relays D and Q would operate but contacts jlZ maintain a loop for relay AA.

When switch CS reaches position I a circuit will be closed for relay B, which as before brings switch CS to rest and closes cam held contacts bcl and 1202. The circuit includes relays D and Q the latter of which operates. Relay D, however, cannot operate in series with relay B. Relay Q at contact (E2) opens the circuit of relay CO. This relay will either hold in an alternative circuit which includes contact 05, or if rclay Q operates before relay C, will re-operate in that alternative circuit.

The system is now ready to respond to a further train of impulses from the calling line which is approaching the extension over the final selector. These impulses are repeated to relay AA which responds thereto and, at contact cal (El) causes switch magnet ASDM to step-wipers AS to a position which depends upon the number, on the party line centre, of the wanted extension. The circuit is, contacts (ml b113, cl, relay C, magnet ASDM. With the switch off-normal, the circult of winding (I) of relay 0 is opened at contacts nl.

When dialling shall be completed, relay AA will be held operated and, consequently, relay C will release and relay BA will be held over winding (I).

Relay C, released, will at contact cl open its own holding circuit through winding (II) at contact 03 (E6) prepare a circuit for motor ME, to cycle alternating current; and at contact 05 open the circuit of relay CO.

Relay CO will release and at contact 003 open the line circuit, whereby relays Q and B will 'release, the latter to connect motor MD to a source of 50 cycle alternating current. At contact'co l (El) relay CO will open the circuit of winding (II) of relay BA which will not, however, release as it has a circuit over winding (I); at contact 008 (E8) it will close a circuit for motor ME; and at contact cod (El l) it will prepare a circuit for relay T.

Motors ME and MD rotate synchronously, and as the former does so, as before it successively closes contacts sm l, sm5, sm6 etc. When eventually that contact sm which corresponds with the position into which switch AS has been set, is closed, relay T operates and at contact tl (E8) earth, contacts fl, i

opens the circuit of motor ME which is thus brought to rest. It also, at contact t9 (E2) closes a circuit for relay CO and at H3 prepares the circuit of relay D; other contacts of relay T need not here be noted.

Relay CO, at contacts col and 002 reverses the line connections, whereby relay B, Fig. l is operated, to arrest the motion of motor MD; at contact 003, completes the circuit for relay D; at contact colt (Elt) prepares a circuit for relay TT; and at contact coll (Ell) opens the circuit of relay T.

Relay D operates and at contact dl (E9) closes a circuit for winding (II) of relay Q.

Relay T releases and, at contact t2 (El 9) closes a circuit which includes contacts coll] and sm3, for relay TT; and at contacts t8 and t3 (E2) opens the circuit for relay CO.

Relay TT (EH3) operates and at contact til closes a holding circuit for itself; at contact 1% (E2) opens the circuit of winding (II) of relay CO; at contacts H5 and ttfi (El) connects ringing current to line AB; and at contact itlii (E2) connects ringing tone to the calling subscriber.

Relay CO on releasing, at contacts col and 002 restores the line connections but at cont-act opens a point in the circuit of relay D; at contact co l opens a point in the circuit of winding (II) of relay BA; at contact 009 (Ell) closes a circuit for relay T which includes a contact sm lsm etc, and at contact col3 (El) prepares a self-drive circuit for magnet ASDM.

Relay T re-operates and at contact t2 closes an alternative holding circuit for relay TT to earth at contact tt2.

When, in response to the ringing current, the called extension replies, relay F will operate and at contact fl (El) remove direct earth from the line; at contact f2 (El) remove ringing tone from wire B2; at contacts f3 and f4 remove ringing current from line A.B.; at contacts f5 and f6 reverse the connection of the line to prepare for the operation of relay R; at contact f'l (El) closes a circuit around contact 003 to provide a circuit for relays D and R; at contact 8 (E8) open the start circuit of motor ME against its restoration; at contact f9 (El) place a short circuit across winding (I) of relay Q to present a balanced bridge; at contact flfl (E9) close a circuit for winding (II) of relay Q; at contact fll (El) removes a short-circuit from across its own winding (II) to provide for its own holding, at contact H2 renders relay AA dependent on contacts d2 and q'l; and at contact fl3 opens the circuit of relay T.

Relay Q at contact ql (El) provides for the holding of relay AA dependent on contact (12, relay D operating sooner than relay Q which has its windin (I) short circuited.

When either party to the connection hangs up the apparatus is restored. Thus, if the calling subscriber hangs up contact a (El) is opened and if the called subscriber hangs up, contact (22 is opened and in either case relay AA is released. When the called party hangs up relay A, Fig. 1, also releases.

Relay AA, at contact aal opens the circuit of relay BA which releases.

Relay BA at contact baii (E'l) closes a circuit for driving magnet ASDM whereby switch AS is self-driven to normal; and at contact ball opens the circuit of relay F.

Relay F, at contact fllJ (E9) opens the circuit of relay Q which, if relay D has also released, releases and at contacts 5 and f6 restores the direction of the line connections.

Relay Q, upon release, at contact q3 (Ell!) opens the circuit of relay TT.

Relay TT, at contact ttfl (E8) closes a circuit for motor ME which restores, and at contact sml, opens its own homing circuit.

The restoration of the direction of current to the line provides a circuit for relay R, Fig. l, which at contact 13 closes a circuit for motor MD, the circuit for relay R including contacts bcl, bdl and 1102.

When switch CS arrives in position I, contacts bcl and Z202 and bdl are opened whereby relay R releases and opens the circuit of motor MD.

The apparatus is now restored to its normal condition.

I claim:

1. In a selecting system, a selecting switch having contacts, an alternating current synchronous driving motor for operating the switch, a plurality of circuits connected to said contacts, means for operating said switch to select one of said circuits, and said switch operated in response to control over one of said circuits.

2. In a selecting system, a selecting switch having contacts, an alternating current synchronous driving motor for operating said switch, and circuit arrangements for operating said motor to continuously operate said switch to successively test the calling or idle condition of said contacts.

3. In a selecting system, a selecting switch, lines accessible thereto, means for operating said switch to connect with said lines, a common line leading to the switch, a pair of devices for con-- trolling the switch, means for reversing current in the common line, one device operated to stop the switch if a calling one of said lines is connected with when the current is in one direction over the line, and the other device operated by current of another polarity independent of the connected with line.

4. In a selecting system, a line, a selecting switch therefor, a synchronous motor operating the switch, a plurality of polarized devices for controlling the motor, and means for connecting opposite polarities of current across the line to cause said devices to operate selectively to start, stop and restart the motor by connecting and disconnecting alternating current thereto.

5. In a selecting system, a selecting switch, a line leading thereto, a plurality of relays in the switch each having a rectifier connected thereto in a different manner, means for connecting said relays to the line at difierent stages in the operation of the switch, and means for reversing the current in the line to control the devices to start, stop and restart the switch.

6. A selecting system as claimed in claim 5 in which the reversal of current in the line is controlled from the switch.

7. In a selecting system, a selecting switch, a common line leading thereto, lines accessible thereto, a synchronous alternating current motor for operating the switch to seize a line, controlled over the common line, and another synchronous alternating current motor at the other end of the common line operating in synchronism with the switch motor to control its operation.

DAVID ADAM CHRISTIAN. 

